(A) captures only part of P2. But it doesn’t capture the additional questions and answers raised in P3 and P4.

This relates only to the question about the size of the okapi population at the beginning of P2. But it doesn’t capture the fact that we have answers to that question, nor does it capture the additional questions raised in P3 and P4.

This best captures the main point. Research has answered some questions (such as how to classify the okapi and the size of its population), but has also raised other questions (such as why they remain in a limited forested area and why they aren’t found in other forest areas).

Too narrow. This doesn’t capture the other questions about okapis discussed in the passage. Also, although the tracking collars helped reveal information about okapi numbers and habits, it’s not clear that the collars revealed that part of the reason okapis appear scarce is their coloration. That would seem to be only a hypothesis offered by the author or zoologists. The role of coloration in apparent scarcity is not a fact that can be revealed by tracking collared okapis.

Not supported, because we don’t know that questions that have puzzled zoologists since okapis were discovered are “mostly” unanswered. We have answers to how to classify okapis and the size of the okapi population. Although some other questions may be unanswered, we don’t know that “most” of them are unanswered.